EPA's Vessel General Permit and Small Vessel General

The uptake and discharge of ballast water potentially transports planktonic (i.e., occur in the
water column) ANS to novel water bodies. Benthic ANS can also be transferred when sediments
are taken in along with ballast water. Ballasting and deballasting occur through openings in
vessel hulls, which are usually covered by protective gates that are permeable to viruses,
bacteria, diatoms, algae, and invertebrate larvae (especially mollusks and crustaceans); however,
corrosion or the loss of these grates permits larger organisms, including postlarval fish, to be
ballasted (Wonham et al. 2000).
On any given day, approximately 7,000 individual species may be “in motion” in ballast tanks
(Carlton 2001), and there is no evidence that ship age, seasonal timing, or age of ballast water
affects the abundance of individuals or species in the ballast tanks (Drake and Lodge 2007).
When species in ballast tanks are transported between water bodies and discharged, they have
the potential for establishing new, non-indigenous populations that can cause severe economic
and ecological impacts to waters of the U.S. It is not possible to quantitatively assess the number
and type of ANS that have the ability to establish a viable population from the 7,000 individual
species currently being carried in ballast tanks (NAS 2011).
It is possible, however, to link past ANS invasions to ballast water (NAS 2011). In the
Laurentian Great Lakes, which are among the best-studied freshwater ecosystems in North
America, 55 – 70% of the 180 ANS invasions are attributed to ballast water release (Ricciardi,
2006; Kelly et al., 2009; Holeck et al., 2004). For coastal marine ecosystems in western North
America, 10-50% of over 250 invasions are attributed to ballast water release (Cohen and
Carlton 1995).
Though the density of organisms in ballast water is just one of many variables that influence the
probability that an invasive species will successfully establish a population in U.S. waters, there
is evidence that significantly reducing the density of organisms in ballast water will reduce the
probability of invasions, when controlling for all other variables (NAS 2011). Thus, establishing
a benchmark discharge standard to reduce concentrations of coastal organisms below current
levels is a logical first step.
Under current U.S. laws, regulations, and permitting requirements, existing best management
practices are required to help reduce the potential impacts of ANS from ballast water discharges.
These include ballast water exchange and saltwater flushing for certain vessels/voyages. These
practices have been shown to offer some protection in mitigating the transfer and potential
introduction of invasive species. While useful in reducing the presence of potentially invasive
organisms in ballast water, ballast water exchange is not feasible for all vessels (e.g., vessels that
cannot voyage offshore), can have variable effectiveness, and in some circumstances may not be
feasible due to vessel safety concerns (Albert et al. 2010).
One way to address these limitations associated with ballast water exchange is to require
treatment of ballast water prior to discharge to meet an established standard for the concentration
of living organisms. On March 23, 2012, the US Coast Guard published final regulations to
phase in ballast water treatment requirements, which became effective on June 21 of that year.
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